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UV-A radiation (320-400 nm) induces modifications to different biomolecules through photosensitized reactions. Oxidized pterins are efficient photosensitizers that accumulate in the skin affected by vitiligo, and photoinduce the oxidation of guanine in a process initiated by an electron transfer from the nucleobase to the triplet excited state of the photosensitizer. In this work, we have investigated the degradation of 2′-deoxyguanosine 5′-monophosphate (dGMP) photosensitized by pterin (Ptr), the parent compound of oxidized pterins, in aqueous solutions under UV-A irradiation. We have identified five products containing the oxidized guanine moiety: the deoxyribonucleoside 5′-monophosphate derivatives of imidazolone, dehydroguanidinohydantoin, guanidinohydantoin, oxazolone and spiroiminodihydantoin. An additional product with a much higher molecular weight, denoted P680, was also detected. The MS/MS analyses show that this compound contains an intact guanine moiety and a modified one. The dependence of the rate of product formation in different experimental conditions was analyzed and a general mechanistic scheme is proposed. Fil: Serrano, Mariana Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Estébanez, Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Vignoni, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Lorente, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Vicendo, Patricia. Université Paul Sabatier; Francia Fil: Oliveros, Esther. Université Paul Sabatier; Francia Fil: Thomas, Andrés Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of pterins present acid-base and keto-enol equilibria. These compounds, under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms, mainly through an electron transfer-initiated process (type-I mechanism), but they also produce singlet molecular oxygen (1 O2 ) upon irradiation (type-II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer.

A new fluorescent compound was isolated from UVA-irradiated aqueous solutions containing pterin (Ptr) and 2′deoxythymidine (dT) in anaerobic conditions. Pterins are widespread in living systems in small amounts, but they are accumulated in some pathological situations. Under UVA radiation, pterins are photochemically active, fluorescent, and photosensitize the generation of singlet oxygen [1O2(1Δg)]. The isolated compound was structurally characterized by using liquid chromatography coupled to tandem mass spectrometry, and its photophysical properties were studied with the time-correlated single-photon-counting technique. The molecular weight and the analysis of the fragmentation correspond to a molecule where the pterinic moiety is attached to the thymine nucleobase. The product exhibits photophysical properties similar to those of Ptr, including relatively high fluorescence and 1O2 production quantum yields., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas